Coherent data structure with multiple interaction contexts for a smart card

ABSTRACT

Data exchange system includes at least one portable data processing unit (5) having data communication elements (14), processing device (15) and memory elements (16). The latter includes an executive program (17) and one or more application descriptions (18(1) . . . 18(n)). Each application description has at least one interaction context (19(1) . . . ) comprising commands, data elements, data references, procedures, access conditions, and external references. The structure of the data elements and the data references, as well as other references, is chosen in such a way that a very efficient use of the restricted memory space of, for example, smart cards is obtained.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 08/676,347, filed Jul. 19, 1996, now U.S. Pat. No. 5,802,519, issued on Sep. 1, 1998, which was the 35 USC 371 national stage of International application PCT/NL95/00055 filed Feb. 8, 1995, which designated the United States.

FIELD OF THE INVENTION

The invention relates to a data exchange system comprising at least one portable data processing unit comprising data communication means, processing means and memory means, the later comprising an executive program.

BACKGROUND OF THE INVENTION

Such a system is known from the international patent application WO-A-87/07063 in which a system for a portable data carrier having multiple application files is described. One of the most important applications of such a portable data carrier is a smart card suitable for multiple applications. The known data carrier is described as a carrier of hierarchically structured data with security features to support multiple applications on the same data carrier. Applications are seen as sets of data. The patent application describes an implementation of an hierarchical file system on a data carrier to store alterable data in combination with an hierarchic set of access permissions. The data carrier responds to a set of common commands. File access permissions are distinct for different operations and granted in dependence on password verification. A password verification attempt counter is introduced as well as the provision of destruction of stored data as sanction against too many attempts of access. The known data carrier is presented primarily as a storage device and not as a processor. Only very simple functions may be performed by the executive program such as binary logic operation. It is not possible to allow the performance of an unspecified set of operations on request of a terminal communicating with the data carrier. The only security option is the introduction of password verification. No other access condition verifications are possible within the known system. Besides, each application of the data carrier has its own file within the memory means of the data carrier. No special measures are taken to enhance the efficiency of the available memory space which, especially on smart cards, is very restrictive and therefore sets limits to the number of possible applications.

EP-A-0,479,655 relates to the implementation of access condition checks in smart cards. One specification technique for that is disclosed, however, it is desirable to provide for measures to include the possibility of other access condition verifications.

EP-A-0,361,491 relates to a chip card programming system to allow protected (re)programming of cards. It describes the use of write-once-access conditions to control access of parts of the programmable memory to be programmed. In this way the number of applications on a single card can be extended. Verification of the access conditions with a variety of techniques including cryptographic protocols is described.

EP-A-0,292,248 relates to loading of applications on a smart card using an unalterable operating system program. It includes the implementation of a data access condition enforcement method using memory zones with assigned access attributes. Specific access conditions are "write-once" (which is only described implicitly) and "execute-only".

U.S. Pat. No. 4,874,935 relates to card programming using a data dictionary where the data dictionary describes the layout of data elements stored in the card's memory. Data dictionaries are commonly understood to differ from directories in that they not only describe data actually stored, but also data which will be stored later. In addition, data dictionaries usually include a description of the data format. In compiled format data dictionaries are used in database management systems where they are stored on the hard disc as part of the database. They are also found in the object load files resulting from program compilation in software development environments. However, the patent does not claim a representation of data dictionaries particularly suited for smart cards.

SUMMARY OF THE INVENTION

The main object of the present invention is to present means to cope optimally with the restrictions imposed by limited physical dimensions of available memory space on portable data processing units, especially smart cards.

A further object of the present invention is to offer a more general mechanism of protected loading of program codes and to allow such a loading for multiple programs each for one application of each portable data processing unit.

Moreover, the present invention is directed to the provision of the use of access condition verifications not prescribed by the manufacturer of the portable processing unit but chosen by the application designer to suit his particular needs.

Therefore the system according to the invention is characterized in that the memory means further comprises at least one interaction context containing the following coherent data structure:

a. a set of basic communication primitives which are accepted whenever the data processing unit communicates with a similar unit, said primitives at least including a primitive used to selectively enter one of the said interaction contexts;

b. a set of procedural descriptions defining the actions to be performed in response to each of the accepted communication primitives, at least comprising a first procedural description to be performed upon activating the interaction context, and a last procedural description to be performed immediately before deactivating the context;

c. a, possibly empty, set of data elements either permanently stored or computed, which are available for use when procedures as defined in the procedural descriptions are performed;

d. a, possibly empty, set of references to data elements, which references are associated to the procedural descriptions, said data elements are also accessible to possibly further interaction contexts and are available for use when procedures as defined in the procedural descriptions are performed;

e. a, possibly empty, data list comprising a list of references to data elements which are available for explicit reference as part of a communication primitive to be used by the procedural description associated with the communication primitive;

f. a set of access conditions associated to the data elements which are referenced in association to the procedural descriptions;

g. a set of access conditions associated to the list of data references in the data list.

By defining data within the memory means of the portable processing unit in such a way the processing unit is really organized as a processor, i.e. it not only allows logical operations but it performs processes which may be loaded in the processing unit by persons authorized to do so, e.g. a staff member of a bank. By providing procedures which may provide arbitrary complex operations in response to received commands and providing an explicit list of stored data elements which are addressable as part of such commands the communication bandwidth can be optimally used; resulting in a reduced number of commands exchanged. With a system according to the invention many actual uses of the system will but require the exchange of two commands. The only thing that is fixed is the structure within the memory means which is defined in such a way that several applications of the unit may be added in a very efficient way, i.e. by using as little additional memory space as possible. This is especially of prime importance if the unit is a smart card which is severely limited as regards available memory space. Besides, the structure according to the invention offers all possibilities to include security measures in order to inhibit unauthorized people from access to processes or data that they are not entitled to use.

In a first preferred embodiment the data exchange system defined above is characterized in that the memory means further comprises at least two interaction contexts, at least one application description and a memory element storing a reference to the interaction context currently being in force, each application description comprising:

a. a data list comprising references to data elements, which references may be accessible to two or more interaction contexts and may be extended by additional data elements;

b. a further set of access conditions associated to said references or to said additional data elements and defining restrictions of use.

By these measures all references to data elements which are common to different interaction contexts are accessible for all those interaction contexts, so they only need be stored once saving memory space. Also common access conditions to said data references are accessible to predetermined interaction contexts. Therefore, also these common access conditions need only be stored once thereby saving memory space and enhancing efficiency.

Each application description may also comprise a procedure library comprising units of executable code which can be used by procedural descriptions of each interaction context associated to each of said application descriptions.

Preferably, the processing unit is suitable for at least two applications with use of little additional memory space. To obtain this object the data exchange system according to the invention is characterized in that the memory means comprises at least two application descriptions and units of executable code which can be used by procedural descriptions of each interaction context within each application description or by each unit of executable code of each procedure library within each application description.

Preferably, the units of executable code in the procedure library are enhanced by including a specification of the use of their operational parameters into classes relating to attributes pertaining to data elements which can be passed as actual value in a computation, which computation only proceeds if the data attributes and parameter classes match. This is an efficient way of verification of access conditions both on data level and on function level for which a very efficient implementation exists.

More reliability of the system is offered if the data exchange system according to the invention is characterized in that the executive program comprises a reference to a default interaction context which is used to initialise the memory element storing a reference to the interaction context currently being in force, in order to carry out a final action after a detection of an internal inconsistency in a recovery to a normal state of operation or whenever the executive program is active and no explicit interaction context has been specified by a communication primitive received from an opposite data processing unit.

In order to enhance the security of data and functions within the processing unit the data exchange system according to the invention may be characterized in that the memory means comprises an interaction context dedicated to comprise Personal identification Numbers and that the executive program is arranged to verify Personal Identification Numbers supplied by a user of the data exchange system.

Advantageously the Personal Identification Number management interaction context and the default context can be implemented as part of the same device holder application. Support of this application by most devices with which a device according to the invention communicates would give the device owner the opportunity to review his personal data as stored in the device memory, for instance a smart card holder could be allowed to modify his PIN at any smart card terminal which provides an appropriate user interface.

Each application description may comprise a list of numeric values which is constructed to provide identifiers for all interaction contexts and comprises at least a first numeric value indicating an application type, a second numeric value indicating a unique identification of the entity providing the application, a third numeric value indicating the nature of the application description and further numbers each uniquely referring to one interaction context associated with the application description.

The string of numeric values uniquely referring to an interaction context provides a means of establishing interoperability between two communicating devices which is more efficient than is currently envisaged for e.g. smart cards in relegating to the application providing entity the responsibility to assign unique values to each interaction context while leaving assignment of unique numbers to entities and application to relevant bodies of sectoral and international co-operation respectively. With benefit the application providing entity can assign the unique context numbers to incorporate implementation version and secret key generation information.

The data communication means may be arranged to structure data exchange in blocks of data comprising at least two parts, a first part being data qualified as operational in that it is used to influence the nature of the operations performed by a command as indicated by a communication primitive or to influence the nature of data resulting from operations carried out, a second part being qualified as security in that it is used to determine the appropriateness of performing an operation or of the acceptability of data within the operational part, to be used in the operation or to prove completion of the operation or correctness of the resulting data.

Such appropriateness, acceptability, proof and correctness being obtained by performing relevant cryptographic operations on the data. Authentication and data protection are thus made an integral part of the command execution providing better security than obtainable in current systems e.g. smart cards.

The executive program may be arranged to perform, upon accepting a communication primitive to perform operations specified in the current interaction context, each operation as part of a predetermined and fixed sequence of actions each of which is specified separately as part of a procedural description associated to the accepted communication primitive, which actions comprise at least the following actions:

a. authorization of the use of the communication primitive;

b. decryption of operational data or any part of it;

c. performing a command with any input data;

d. encryption of any operational data resulting from any operation performed;

e. computation of a proof of completion of any performed action or of correctness of the resulting data to be used in security computations.

Security is further enhanced if the data processing unit generates a random transaction number upon initializing data transfer, which serves as basis for cryptographic computations.

To provide for a possibility to enter a new interaction context if required one communication primitive may be assigned a specified value which will always be interpreted as a request to enter a new interaction context.

In a further preferred embodiment the data exchange system according to the invention is characterized in that it comprises a further data processing unit comprising the same elements as the data processing unit as well as an application programmers interface which consists of program code designed to allow additional computer programs to be implemented to give users control over the sequence of exchanged communication primitives or to influence the data transferred in them or to learn or further process the data received in the exchange. Development of software for systems according to the invention will benefit from the availability of an application programmers interface.

In such a preferred embodiment of the invention the primitive used to enter a specified interaction context may comprise numeric values to be used in security calculations in subsequent communications, a first value generated at random by one of the processing units and a second value serving to identify said one processing unit.

To further benefit from the current invention, each communication primitive may further be structured to consist of two or more numeric values which enhance the expressive power of the communication primitive for interpretation by the executive program.

As a first alternative, each communication primitive may be composed of two or more numeric values, a first value being used to refer to a procedural description of an action associated to the communication primitive, a second value being composed of a fixed number of binary values each of which is interpreted by the executive program as a reference to a single data element.

As a second alternative, each communication primitive may be composed of two or more numeric values, a first value being used to refer to a procedural description of an action associated to the communication primitive, a second value being used to determine which of the data elements available for external reference in an active interaction context will be used while performing responding actions in such a way that any data element is selected if it contains a value that matches said second value.

As a third alternative, each communication primitive is composed of two or more numeric values, a first value being used to refer to a procedural description of an action associated to the communication primitive, a second value being composed of a number of binary values which are assigned specific meanings by the executive program to be used in interpreting data formats in the communication primitive and in performing responding actions.

The context mechanism defined above and the techniques it makes available leads to a wider range of smart card use and an approach of smart card application development which have a number of advantages over the traditional ways.

First of all, it allows the execution of application specific program code in a smart card without the need to thoroughly examine the code for potential threats to the security of data stored for other applications. As the access conditions which are stored with the data on the card are enforced by the card operating system without possibility of outside interference during execution of application code, a multi application card scheme does not need a program code vetting authority. Such authority is the only way to allow a private code execution facility in traditional smart cards. By approving code for execution on a card a vetting authority incurs liabilities with respect to the overall system security; it makes the management of multi application smart card schemes much more complex. The associated complexity and costs sake application specific code in traditional card schemes almost infeasible. With the new technique the demand for this facility from smart card application providers which has been there for some time can be met.

Secondly, as direct consequence of protected application of specific programs in cards, a specific application can be implemented that is dedicated to load other applications in the card. In this way, the applications once loaded in a card can be protected from the very application that loaded them. This protection gives parties involved in a multi application card scheme especially the card issuing entity and the application providing entities a basis for their business agreement. Being based on tangible things as the amount of storage needed on each card, the number of cards to be equipped and the duration of the application on the card instead of an abstract notion of "trust" and "good care" the application providers contract is easier to formulate than in traditionally implemented smart cards. Moreover, the card issuer and application provider do not need to share secret keys and protect this sharing with contractual obligations and mutually agreed key transportation facilities.

Thirdly, the application software if implemented based on the new technique has several benefits compared with prior art smart card operating systems:

A minimal exchange of data between a terminal and a card is needed to establish interoperability between card and terminal, e.g. they support the same application(s). Values of data to be exchanged to this end can be structured as proposed in the draft international standard ISO 7816-5;

To complete a transaction between card and terminal the minimal number of data exchanges as theoretically inferred can actually be used, because the transaction is completed as a private computation, instead of the necessity to use a lengthy sequence of standard commands;

It allows controlled access to data without requiring an involved access path dictated by a directory and file hierarchy shared by all applications as currently in use and proposed for standardisation;

It allows the development of the terminal and smart card application in tandem, which development process can be supported with computer software tools such as compilers and emulators. Design and implementation of card and terminal software can thus be lifted above the tedious and error prone assembly language coding currently required;

It allows standardization of equipment, both cards and terminals, using an abstract formalism to describe the device capabilities which gives flexibility towards future developments, such as new features offered by card or terminal manufacturers. The standardized terminal capability could include an API. In contrast current standardization efforts in smart cards concentrates on prescribing fixed data contents of messages to provide identification values to be interpreted in a way as determined by the standard, which leaves little room for new developments.

Finally, with the new technique implementors of smart card operating systems are given great freedom of designing optimal implementations of the card's operating system kernel and terminal operating system. Smart card hardware designers are given several options to optimize chip silicon use with hardware support for basic operation included in the system kernel. Hardware cost reduction obtained starting with the specialized design defined above can be greater than when based on improvements on general purpose single chip computers.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in detail with reference to some drawings which show an example of the implementation of the general principles of the present invention.

FIG. 1 shows a prior art application design on smart cards based on an hierarchically organized collection of data elements;

FIG. 2 presents a diagram of the communication flow between a portable processing unit and a similar structured processing unit in a format currently accepted as standard;

FIG. 3 presents a basic implementation of the present invention using the concept of interaction contexts in portable processing units, such as smart cards, and card terminals;

FIG. 4 presents an example of a practical organization of an execution context, highlighting different relationships between procedural descriptions contained in the interaction context and data elements and library functions used while performing the procedures;

FIG. 5 shows an example of a flow diagram of program execution control and security context switches involved in performing the procedural description invoked by a communication primitive.

DETAILED DESCRIPTION OF THE INVENTION

The structure of data and files in prior art systems is depicted in FIG. 1. Basically there is a master file 1 which is connected to several elementary files 3 and one or more dedicated files 2. Each dedicated file 2 may be connected to one or more further dedicated files 2 and to one or more elementary files 3. The prior art uses a tree-like hierarchy of directories and files. The number of subordinate levels in the prior art structure is in principle unlimited. The terminology used in FIG. 1 is taken from the international proposed ISO standard 7816-4. According to the standard format for communication flow between a portable data processing unit 5 and a similar structured data processing unit 4, as shown in FIG. 2, the communication comprises a set of pairs of blocks. The communication starts with a reset signal m.0. from the data processing unit 4. Such a reset signal may be outside the communication bandwidth such as generated by power-on-logic in data processing unit 5. The portable data processing unit 5 responds with an answer to reset (ATR) signal m1 possibly followed by contents. All subsequent pairs of blocks m2, m3, . . . , m(n-1), mn consist of blocks headed by a communication primitive (e.g. a command) followed by contents.

FIG. 3 shows the internal structure of two data processing units according to the invention which are communicating with each other by transmitting and receiving data. The left data processing unit 4 may be, among others, a terminal and the right data processing unit may be, among others, a portable data processing unit, e.g. a smart card. However, the invention is also applicable to two portable data processing units able to communicate with each other by appropriate communication means.

Each of the data processing units 4, 5 comprises data communication means 7, 14 through which structured blocks of data can be exchanged. Each of the data processing units 4, 5 comprises processing means 8, 15, and memory means 9, 16. The memory means 9, 16 could be any configuration of read-only memory (ROM), random access memory (RAM) and programmable read-only memory such as electrically erasable programmable read-only memory (EEPROM).

The memory means 9, 16 comprises an executive program 12, 17, here indicated by "MAXOS". If the portable data processing unit 5 is suitable for two or more applications, the memory means 9, 16 comprises two or more application descriptions 13(1) . . . 13(n), 18(1) . . . 18(n). There are as many application descriptions as there are applications of the data processing unit concerned. Each application description is indicated by "CSA". The second application description 13(2), 18(2) has been shown on an enlarged scale in FIG. 3 to allow display of the contents of each application description. Each application description 13(i), 18(i) comprises at least one "interaction context" 11(1) . . . 11(m), 19(1) . . . 19(m). Each interaction context is indicated by "CTA". The first of these interaction contexts 11(1), 19(1) has been shown on an enlarged scale to allow display of their contents. Each interaction context contains:

a set of commands specifying the communication primitives recognized by the interaction context and referencing appropriate procedures specified in a set of procedures;

a set of data;

a set of data references to date residing in other interaction contexts if any;

a set of procedures that may be performed by the executive program 12, 17;

a set of access conditions to the data elements;

a set of external references referring to data elements to be used in commands issued by the other data processing unit;

optionally, developer specified other lists.

Finally, the memory means 9, 16 comprises a memory element 21, 20 that contains a reference to the "current CTA", i.e. the interaction context currently in force.

The intention of several interaction contexts within one application description is to provide a functional separation in possible interactions between the data processing units 4, 5. This is especially relevant when the functional separation is also a separation in security conditions. An example may be a first interaction between a smart card and a terminal to open, for instance, a door and a second interaction when programming doors that are allowed to be opened. The second interaction needs a better security than the first interaction and is assigned its own interaction context. To obtain access to the interaction context is the first step in assuring the security of the operations that may be executed within the interaction context.

FIG. 4 shows a practical approach to implementation of the context mechanism displayed as a memory organization model which shows the relations between data elements, access conditions and procedures. The structure of FIG. 4 applies whenever there are two or more applications of the portable data processing unit 5. If there is only one application the structure is strongly simplified, as will be explained later. In FIG. 4 the reference numbers of the data processing unit 5 are depicted. However, the structure of FIG. 4 is likewise applicable to the memory means 9 of the data processing unit 4. In FIG. 4 data element descriptions and procedure descriptions are optimally organized to reflect sharing of program code and sharing of data between different interaction contexts (CTA's) which make up one application (CSA).

The memory means 16 comprise data elements H(1) . . . H(7), executable code elements G(1) . . . G(5) which are part of the operating system, and application descriptions 18(1), 18(2) (CSA1, CSA2). In FIG. 4, data and code which are internal to the operating system are left out. The number of data elements, executable code elements and application descriptions as presented in FIG. 4 is only given by way of example: the numbers may vary as required in reality.

Each application description 18(1), 18(2) is physically present in the memory means. They provide a first bottom layer of abstraction to reflect memory use. Each application description 18(1), 18(2) consists of:

a procedure library consisting of units of executable code F(1) . . . F(4) that may refer to units of executable code of the operating system made available for this purpose, as indicated by arrows p(1) . . . p(5);

a list of data elements E(1) . . . E(7) to be used by procedures within the interaction contexts 19(1) . . . 19(2) within the present application description 18. This data list comprises data access conditions and pointers q(1) . . . q(7) to storage areas holding data elements;

an interaction context list comprising a number of interaction context descriptions 19(1), 19(2).

The number of elements within the procedure library, the list of data elements and the interaction context list within the application description 18(1) as shown in FIG. 4 is for presentation purposes only. Of course, the number of elements may vary depending on the desired application.

Interaction contexts 19(1), 19(2) are physically present in the memory means storing the application description 18(1). Logically, the interaction contexts provide a second layer of memory use control. The combined control provided by this second layer and the application description layer gives an effective implementation of an execution context mechanism for portable data processing units, such as smart cards. Each interaction context 19(1), 19(2) comprises:

a list of procedural descriptions C(1) . . . C(5). These procedure descriptions may refer to procedural descriptions in the procedure library within the application description 18 as indicated by example arrows s(1), s(2). Alternatively these procedural descriptions may refer to executable code elements G(1) . . . G(5) provided by the operating system, as indicated by example arrow t(1). As a further alternative these procedural descriptions may contain explicit references to any data elements which are used by the procedure during execution and which are present in the data list of the application description 18 concerned, as indicated by arrows r(1) . . . r6);

a data list containing data elements B(1) . . . B(5) exclusively available for use by the procedures in the interaction context concerned. Data elements are represented as references to the data list of the application description 18 concerned with associated access conditions to adhere to when accessing the actual data, as indicated by arrows u(1) . . . u(5);

an external interface list comprising communication primitives A(1) . . . A(4) which are accepted as commands by the interaction contexts 19(1), 19(2) concerned. Each command within a communication primitive refers to a member of the procedural descriptions C(1) . . . C(5) of the procedure list within the interaction context concerned, as indicated by arrows v(1) . . . v(4). The commands when issued by the communicating device 4, may refer to elements in the data list of the application description by one or more addresses following the command. Each command may be accompanied by data elements as input to the command processing. The number of addresses as given here is by example only and is determined for each command as required in reality.

Protection of data elements is provided for by the provision of access conditions. Any external command within a communication primitive A(1) . . . A(4) can only address data elements referenced in the data list of the interaction context 19 concerned. Access is only allowed if the access conditions are met. These access conditions specify the type of access that is allowed for the command; such an access condition may be no access, read-only access, read-and-write access, and secret key use. Other access conditions may be applied too. For example, the command of communication primitive A(1) may have read-only access to data element B(2) through reference arrow w(2), while the command of communication primitive A(2) has read-and-write access to the same data element B(2) through reference arrow w(3).

Procedural descriptions C(1) . . . C(5) can refer to data elements in the data list of the application description 18 concerned and no others. Again, access is only provided if the access condition is met. These access conditions also specify the type of access that is allowed: for instance, no access, read-only access, read-and-write access, and secret key use. Access conditions for different procedural descriptions within the same interaction context 19 may differ for the same application description data list element E(1) . . . E(7), e.g. reference arrow r(1) may represent a read-only access condition, whereas reference arrow r(2) may represent a read-and-write access condition.

Access conditions are checked on the relevant level, i.e. application description level or interaction context level and only once. An element B(1) . . . B(5) of the data list within an interaction context 19(1), 19(2) refers directly by arrow u(1) . . . u(5) to the pointer of a data element in the data list of the application description 18(1) because the access conditions are already met in the data list element E(1) . . . E(7) of the application description 18(1). Procedural descriptions C(1) . . . C(5) within an interaction context 19(1), 19(2) which refer to data list elements within application description 18(1), however, have to first meet the access condition associated with the data list elements E(1) . . . E(7) within the application description 18(1). Any data elements or procedural description elements within the data lists of the application description 18(1) and its associated interaction contexts 19(1), 19(2) cannot be referred to by any other application description within the memory means 16. The executable code which constitutes the procedural description can only address data by indirection via the restricted set of data references associated with each of the procedural descriptions C(1) . . . C(5). Using data elements described by B(1) . . . B(5) the list of references is temporarily extended by the executive program with references to data element as obtained by evaluating addresses which are actually specified in the communication message accepted as the command associated with the procedural description. Thus no other data can be accessed than explicitly specified, and only observing specified conditions of use. In other words, the preferred memory reference model of FIG. 4 as regards the application description with its associated interaction contexts provides an exclusive context for operations within one single application of the data processing unit 5. Data elements H(1) . . . H(7) are stored in the memory means 16 common to all applications but contain data for exclusive use within the context of application description 18(1), such exclusivity is guaranteed by the executive program in allowing existance of a single pointer to each storage location such as q(1) from E(1) to H(2). Only the code elements G(1) . . . G(5) may be referred to by any of the application descriptions 18(1) . . . stored within the memory means 16. These last references of other application description than application description 18(1) to the common codes G(1) . . . G(5) are not explicitly indicated in FIG. 4. However, any person skilled in the art can easily extend the structure of FIG. 4 to two or more application descriptions 18(1), 18(2), . . . .

After having explained how data elements may be protected by the use of access conditions of different kinds, now, memory management provisions will be explained. For memory management, it is desirable that alterable data (data elements) and not alterable data (operating system code) can be managed by the operating system separately. The memory reference model as shown in FIG. 4 provides a separation of code and data elements within the memory means 16 which are referred to by pointers q(1) . . . q(7), p(1) . . . p(5) from the data list and the procedure library, respectively, within the application description 18 concerned. Data list elements within each interaction context 19(1), 19(2) only contain references to these pointers and no direct references to the codes G(1) . . . G(5), and the data elements H(1) . . . H(7) within the memory means 16. The data list of the application description 18 concerned provides the level of indirection repaired by the operating system to perform memory management.

Code duplication is avoided by providing common code libraries on two levels: "command bodies" like procedural description C(3) which refer to code element F(2) in the procedure library in application description 18(1) in order to share common codes among different interaction contexts. However, the body of procedural description C(3) also refers directly to a code G(3) stored in the memory means 16 and provided by the operating system. All units of executable code G(1) . . . G(5) provided by the operating system are implemented for efficient execution.

Fundamentally, the memory structure according to FIG. 4 is also applicable in situations where only one application of the data processing unit 5 is provided for. In that case the only application description 18(1) may even coincide with one interaction context 19(1), which interaction context then contains at least the following coherent data structure:

a. a set of basic communication primitives A(1) . . . which are accepted whenever the data processing unit 5 communicates with a similar unit 4, said primitives at least including a primitive used to selectively enter one of the said at least one interaction contexts;

b. a set of procedural descriptions C(1) . . . defining the actions to be performed in response to each of the accepted communication primitives A(1) . . . , at least comprising a first procedural description to be performed upon activating the interaction context, and a last procedural description to be performed immediately before deactivating the context;

c. a, possibly empty, set of data elements H(1) . . . either permanently stored or computed, which are available for use when procedures as defined in the procedural descriptions C(1) . . . are performed;

d. a, possibly empty, set of references to data elements, which references are associated to the procedural descriptions C(1) . . . , said data elements are also accessible to possibly further interaction contexts and are available for use when procedures as defined in the procedural descriptions C(1) . . . are performed;

e. a, possibly empty, data list comprising a list of references to data elements which are available for explicit reference as part of a communication primitive to be used by the procedural description associated with the communication primitive;

f. a set of access conditions associated to the data elements which are referenced in association to the procedural descriptions;

g. a set of access conditions associated to the list of data references B(1) . . . in the data list.

If there is only one application provided for the data processing unit 5 and there are at least two interaction contexts 19(1), 19(2) each application description comprises:

a. a data list comprising references E(1) . . . to data elements, which references may be accessible to two or more interaction contexts 19(1) . . . and may be extended by additional data elements;

b. a further set of access conditions associated to said references E(1) . . . or to said additional data elements and defining restrictions of use.

The set of procedural descriptions in each of the two or more interaction context descriptions also contains an additional last procedural description to be performed immediately before deactivating the context.

FIG. 5 represents the flow of control in the executive program defined above by "MAXOS" (12,17).

After powering the system the software starts with processing a reset code in step 30. In step 31 the kernel operations security level of the data processing unit is entered. The access conditions describing this level are stored in an unmodifiable part of memory, e.g. ROM or hardware logic. In step 32 the non-volatile memory is checked for consistency and any modifications which might have been left unfinished by sudden power down, e.g. by extraction of a smart card, are cancelled. Non-volatile memory consistency check only involves examining state information stored in memory and computing check sums. The content of memory, if accessed at all, is only used to compute check sums. Thus, the consistency check is a safe operation. The exact nature of the consistency check facilities depends on details of hardware within the data processing unit and non-volatile memory modification routines which are to a wide extent irrelevant to the specified security architecture. After the general memory consistency check the pre-computed levels of the security context stored in the memory are verified. Finally, the random access memory of the data processing unit is initiated.

In step 33, if the executing environment is thus declared safe, the secure application security level of the data processing unit is entered. In this level any access to memory pertaining the kernel operations is blocked. Access to application data and description from this level is exclusively provided through routines in the kernel which maintain state information on ongoing memory operations.

Upon first entry after reset, in step 34 application data element descriptors are used to check consistency of stored data with the descriptor and memory is changed if in a state inconsistent with the attribute as described. An answer to reset (ATR) message is composed from application identifiers stored in the application descriptors and completed with a transaction number computed to be unpredictable by the receiving other data processing unit 4. Internal to the data processing unit a terminal command is generated to activate a default interaction context. Directly after the ATR message is sent to the other data processing unit 4 this internal context activation command is executed to provide an interaction context for subsequent commands. The ATR message clearly indicates the readiness of the data processing unit 5 to accept further commands. The default interaction context can be designed as part of a "smart card holder application" which is present as one standard application in all multi-application smart cards. In this specific application context the user, i.e. the smart card holder, can review his personal data or open any of the other applications on the card.

In step 35, as result of the context activation command, the interaction context (CTA) security level is entered for the standard smart card holder CTA.

After an application has been activated completely it is ready to receive commands from the other data processing unit 4. Further processing depends on the command received: a command to activate an application is handled different than a command which is to be executed. Therefore, in step 38, after having established that a communication primitive is received in step 36 and is established to be acceptable in step 37, it is tested whether a new application has to be activated. If not, step 39 is entered in which the command is checked to determine whether it is allowed and the input data can be accepted. These checks are performed for a command only if specified in the application descriptor. Also a decryption of input data may be carried out in step 39.

If the test succeeds the "data access protection level" is entered, step 40. On this level, the highest security level, routines may be executed which are coded by application providers, step 41. Such routines are stored in the application descriptor and function as an application specific reaction to a specific command issued by the other data processing unit 4. This security level constrains memory access to a subset specifically defined for the command being executed.

After carrying out the command with the submitted input data in step 41, the data access protection level is left, step 42.

Output data and (cryptographic) proof of command completion is generated in step 43. After step 43 the program waits for new communication primitives, step 36.

If no special command routine is defined and the command can be executed by procedures consisting solely of operating system functions the data access protection level (step 40) is not entered, and the command will be performed on the interaction context security level directly as the operating system routines are designed not to violate any data protection.

If, in step 38, it is established that no new application is to be activated the program proceeds with step 44 in which a context de-activation procedure is performed. In step 45 the current application specific security level is left and, in step 46, within the security level of the executive program "MAXOS" the data accompanying the command are checked.

If the command is allowed by proper authentication as specified for the requested application a new application specific CTA security level is entered, step 47. This level restricts access to data pertaining to the newly opened application.

The data processing unit 5 produces data in response to a context activation command by executing an initialization instruction as defined in the procedure list, step 48. If such an application provider coded routine is present the data access protection level is entered in step 49. The context activation procedure is performed in step 50. In step 51 the data access protection level is left and the response is communicated to the other data processing unit 4 and the data processing unit 4 itself is ready to receive a new command after step 43, specified above.

After having described the FIGS. 1 to 5, now some general remarks to the data exchange system according to the invention are made.

The codes in the procedure library within each application description 18(1), 18(2) may be enhanced by including a specification of the use of their operational parameters into classes relating to attributes pertaining to data elements which can be passed as actual value in a computation, which computation only proceeds if the data attributes and parameter classes match. This provides one way to verify access conditions both to data elements and to functions. Comparing properly encoded bit maps of data attributes and parameter classes respectively may provide an efficient implementation for this additional technique.

The executive program 12, 17 may comprise a reference to an interaction context which is used to initialize the current interaction context in the memory element 20 storing a reference to the interaction context currently being in force. By this measure it is possible to carry out a final action after a detection of an internal inconsistency in a recovery to a normal state of operation or whenever the executive program 12, 17 is active and no explicit interaction context has been specified by a communication primitive received from the other data processing unit 5. This default interaction context may well be one such context contained in the cardholder application as described above.

Additionally, the memory means 9, 16 may comprise an interaction context 11, 19 dedicated to comprise personal identification numbers (PIN's) and the executive program 12, 17 is arranged to verify personal identification numbers supplied by a user of the data exchange system. Several such personal identification numbers, passwords, may be used. One such password may be used to protect use of the device in transactions where privacy sensitive data can be revealed. A second password may be used to protect transactions where data representing a value payable by the password holder is communicated. A third password may be used to protect transactions where operations are performed deemed critical to the security of the application such as modes of protection being called upon as specified within each of the interaction contexts 11, 19 that may require it. Further passwords may be provided for. This PIN management interaction context may well be one such context contained in the card-holder application as described above.

Each application description 13, 18 may comprise a list of numeric values which is constructed to provide identifiers for all interaction contexts 11, 19 and each application description 13, 18 may comprise at least a first numeric value indicating an application type, a second numeric value indicating a unique identification of the entity providing the application, a third numeric value indicating the nature of the application description 13, 18 and further numbers each uniquely referring to one interaction context 11, 19. The first two numbers may be assigned according to rules well established in the trade, whereas the remaining numbers may be chosen by the application providing entity as deemed appropriate. Especially it may assign numeric values to distinguish between different version of the implementation or to identify the generation of the set of cryptographic keys employed by the application in its cryptographic computations. Additionally, the device ray include in the answer to reset message a list for each of the interaction contexts 11, 19 contained in its memory means an identification number composed of the unique identification values stored with the interaction context. The first element in the list of interaction context identification numbers may be an identification for the default context.

The data communication means 7, 14 are preferably arranged to structure data exchange in blocks of data. These blocks of data comprise at least two parts, a first part being data qualified as operational in that it is used to influence the nature of the operations performed by a command as indicated by a communication primitive or data resulting from operations carried out. A second part will be qualified as security in that it is used to determine that appropriateness of performing an operation or of the acceptability of data within the operational part to be used in the operation or to prove completion of the operation or correctness of the revealed data.

When the data is structured in this way the executive program 17 may be arranged to perform, upon accepting a communication primitive to perform operations specified in the current interaction context 20, 21, each operation as part of a predetermined and fixed sequence of actions, each of which is specified separately as part of a procedure description rule associated to the accepted communication primitive. A first action may be specified as a function to authorize the use of the communication primitive at this point in the sequence of communications. A second action may be specified as a function to decrypt the operational data or any part of it, whereas a third action may be specified as the operational procedure proper. A fourth part may be specified to encrypt any operational data which results from the operations performed and a fifth action may be specified as a function to compute a proof of completion of the performed action or of correctness of the resulting data or to be used in security computations in the receiving data processing unit. These actions are reflected by the flow diagram of FIG. 5.

Additionally, the data processing unit 5 may include in its answer to reset message a number chosen to be unpredictable in value by the receiving data processing unit 4, which can serve as the basis for cryptographic computations. Such a number may be designated as the "card transaction number".

There will be provided for one communication primitive assigned a specified value which will always be interpreted as a request to enter a new interaction context 11, 19. This communication primitive may be designated as the "activation command". The data accompanying the activation command sufficiently specifies the context to be activated possibly by referring to the identification numbers communicated as part of the answer to reset message. The actions performed in responding to the activation command are firstly described by the procedural description contained in the context accepting the primitive designated as for deactivation and secondly described in the procedural description designated for activation contained in the context specified as to be entered.

Preferably the communication primitive used to enter a specified interaction context 11, 19 comprises numeric values to be used in security calculations in subsequent communications. A first random value may be generated by one of the processing units 4, 5 and a second value may serve to identify that one processing unit. This identification might be the result of computations, which are such that the resulting value sufficiently identifies the device and the state of its memory as required by computations or other actions which might be done in subsequent exchanges of data in the interaction context 11, 19 to be activated. Said second value may be designated as "terminal identification".

Additionally, the activation command gives as part of the resulting data a numeric value serving to identify the particular responding data processing unit sufficiently as required by computations or other actions which might be done in subsequent exchanges of data in the context just being activated, which number may be designated as "smart card identification".

Besides the smart card identification number may be computed using cryptographic functions from data stored in the data processing unit 5 or from the data received as part of the activation command in such a way that the number varies in unpredictable manner when computed in response to activation commands received from initiating devices with differing terminal identification numbers; a smart card identification thus computed can be designated as the "smart card pseudonym". Moreover, before performing the actions described in the procedural description of the activation procedure of a context to be entered the executive program may perform a cryptographic computation specified as part of the procedural description in that context designated to be performed upon activation to determine whether the context may be activated. The computations may involve use of the smart card transaction identification, terminal transaction identification and terminal identification and other values stored in the memory means.

As an alternative to such specific computations supported with specific data in performing commands, commands with bitfield specification of referenced data elements may be used. Then, each communication primitive is composed of two or more numeric values, a first value being used to refer to a procedural description of an action associated to the communication primitive, a second value being composed of a fixed number of binary values each of which is interpreted by the executive program 12, 17 as a reference to a single data element. This data element is specified in the list of external data references in the interaction context 11, 19 concerned, each data element in the list being specified by the presence of a binary value of one of the binary numbers in a corresponding position in the list of binary values. This second value may be designated as the "operand addresses". Each of the data elements which are so specified are made available by the operating executive program 12, 17 to be used in the responding action in a manner as may be described in the procedural description of that action.

As an alternative to specific computations with specific date and commands with bitfield specification of referenced data elements a command format with data match specification of data elements may be applied. In that case, each communication primitive is composed of two or more numeric values, a first value being used to refer to a procedural description of an action associated to the communication primitive, a second value being used to determine which of the data elements available for external reference in an active interaction context 12, 19 will be used while performing responding actions in such a way that any data element is selected if it contains a value that matches said second value. This second value may be designated as the "operand tag specifier". Additionally, the interaction context 11, 19 may contain a procedural description indicating in what way an operand tag specifier given as part of a command is to be compared with data contained in any of the data elements available for external reference in that context, which procedural description is performed to select the intended data elements before the procedural description is performed specifying the command actions proper.

As a further alternative a command format with bitfield specification of command interpretation may be used. Then each communication primitive is composed of two or more numeric values, a first value being used to refer to a procedural description of an action associated to the communication primitive, a second value being composed of a number of binary values which are assigned specific meaning by the executive program 12, 17 to be used in interpreting data formats in the communication primitive and in performing responding actions. Here the second value may be designated as "command modifier". The values are recognized for their assigned meaning by all units equipped with this additional technique.

In case the latter alternative is applied the command modifier may include a binary value which determines whether a third part of the command is to be used as operand address or as operand tag specifier. However, the command modifier may, as an alternative, include a binary value which determines whether the operation performed as response to the command will use data as one data element or is composed of a concatenation of data elements one to be processed in conjunction with each data element specified as part of the command value using operand addresses or the operand tag specifier. Alternatively, the command modifier may include a binary value which determines whether data provided with the command is encoded using the tag-length-value method to discriminate successive concatenated data elements.

A further option is that the command modifier may include a binary value which determines whether performing the action implied by the command will actually lead to effective change of data stored in the data processing unit 5 (smart card) or actually result in data computed by the data processing unit 5, or that the command result is data reflecting the state of the unit with regard to the acceptability of the command, the data accompanying it, the size of the data which could result from computations or other sundry attributes.

In short, the new technique introduced above especially suitable for implementation in smart cards is the concept of a separate execution environment. In this approach the processing means and other resources in a computer are shared between different applications as if the application was the only user of the computer. Building on this new technique in smart card implementations in addition a mechanism is provided to define multiple access conditions for data shared by a number of related applications. A second technique supported by the separate execution environments and introduced above is the possibility to define the functional meaning of commands in each environment to obtain a minimum number of commands in each interaction between two similar data processing units 4, 5 within a data exchange system. Finally it is possible with the new technique for names referring to stored data elements to be assigned within each context separately. The reference to stored data elements as part of a command received from one of the data processing units 4, 5 can thus be made very efficient: due to the very small number of data elements and small number of distinct operations that is used in today's smart card practice in each environment separately only a few bits are needed to encode the name and instruction space. In a similar fashion access conditions, methods of verification thereof and cryptographic operations available to that end in actual smart cards will be very restricted in number and they can be expressed very efficiently in the two tier hierarchy of interaction context descriptions 19(1) . . . enclosed in application description 18. 

What is claimed is:
 1. A computer data signal embodied in a carrier wave comprising a, possibly empty, set of data elements and a structure for data that define modes of communication among data processing units, the structure comprising:first access conditions controlling access to the data elements in the set of data elements; an external interface list having at least one communication primitive that is a defined value and accepted as a command upon receipt by a one of the data processing units and a first set of data references; a procedural list having at least one procedural description defining procedures to be performed by the one data processing unit using the set of data elements in response to the at least one communication primitive; a, possibly empty, second set of references to the set of data elements, the second set of references being associated with the at least one procedural description and the first access conditions such that the set of data elements is available for use when the procedures defined in the procedural descriptions are performed and the first access conditions are met; and a, possibly empty, data list comprising second access conditions controlling access to the data elements in the set of data elements and a third set of references to the set of data elements, the third set of references being available as targets for the first set of data references through the second access conditions, the data elements referenced by the third set of references being used by the at least one procedural description associated with the communication primitive.
 2. A computer readable medium having stored therein a, possibly empty, set of data elements that are either permanently stored or computed and a structure for data that define modes of communication among data processing units, the structure comprising:first access conditions controlling access to the data elements in the set of data elements; an external interface list for storing at least one communication primitive that is a defined value and accepted as a command upon receipt by one of the data processing units and that includes a first set of data references; a procedural list storing at least one procedural description defining procedures to be performed by the one data processing unit using the set of data elements in response to the at least one communication primitive; a, possibly empty, second set of references to the set of data elements, the second set of references being associated with the at least one procedural description and the first access conditions such that the set of data elements is available for use when the procedures defined in the procedural descriptions are performed and the first access conditions are met; and a, possibly empty, data list comprising second access conditions controlling access to the data elements in the set of data elements and a third set of references to the set of data elements, the third set of references being available as targets for the first set of data references through the second access conditions, the data elements referenced by the third set of references being used by the at least one procedural description associated with the communication primitive.
 3. A memory for a data processing unit for storing data defining modes of communication between data processing units, the memory having stored therein a data structure that comprises at least one application program and a, possibly empty, set of data elements that are either permanently stored or computed,the at least one application program comprising at least one interaction context that define the modes of communication and comprising first access conditions controlling access to data elements in the set of data elements, the at least one interaction context comprising:an external interface list for storing at least one communication primitive that is a defined value and accepted as a command upon receipt by the data processing unit to enter the one interaction context and that includes a first set of data references; a procedure list storing at least one procedural description defining procedures to be performed by the data processing unit using the set of data elements in response to the at least one communication primitive; a, possibly empty, second set of references to the set of data elements, the second set of references being associated with the at least one procedural description and the first access conditions such that the set of data elements is available for use when the procedures defined in the at least one procedural description are performed and the first access conditions are met; and a, possibly empty, data list comprising second access conditions controlling access to the data elements in the set of data elements and a third set of references to the set of data elements, the third set of references being available as targets for the first set of references through the second access conditions, the data elements referenced by the third set of references being used by the procedural descriptions associated with the communication primitive.
 4. The memory of claim 3, wherein the memory has stored therein first executable program code elements of the procedures defined in the procedural descriptions, and wherein the at least one application program further comprises second executable program code elements of the procedures defined in the procedural descriptions, the second code elements being associated with the procedural descriptions, the first code elements being associated with at least one of the second code elements and the data list.
 5. The memory of claim 3, wherein at least one of the data processing units is portable, and wherein the memory is in the portable one of the data processing units.
 6. The memory of claim 3, wherein the application program includes a further interaction context.
 7. The memory of claim 3, wherein the memory has stored therein a further application program.
 8. The memory of claim 7, wherein each application program includes a plurality of interaction contexts.
 9. A memory for a data processing unit for storing data defining modes of communication among data processing units, the memory having stored therein a, possibly empty, set of data elements that are either permanently stored or computed and a data structure that defines the modes of communication and that comprises:first access conditions controlling access to the data elements in the set of data elements; an external interface list for storing at least one communication primitive that is a defined value and accepted as a command upon receipt by the data processing unit and that includes a first set of data references; a procedural list storing at least one procedural description defining procedures to be performed by the data processing unit using the set of data elements in response to the at least one communication primitive; a, possibly empty, second set of references to the set of data elements, the second set of references being associated with the at least one procedural description and the first access conditions such that the set of data elements is available for use when the procedures defined in the procedural descriptions are performed and the first access conditions are met; and a, possibly empty, data list comprising second access conditions controlling access to the data elements in the set of data elements and a third set of references to the set of data elements, the third set of references being available as targets for the first set of data references through the second access conditions, the data elements referenced by the third set of references being used by the at least one procedural description associated with the communication primitive.
 10. The memory of claim 9, wherein the memory has stored therein first executable program code elements of the procedures defined in the procedural descriptions, and wherein the data structure further comprises second executable program code elements of the procedures defined in the procedural descriptions, the second code elements being associated with the procedural descriptions, the first code elements being associated with at least one of the second code elements and the data list.
 11. The memory of claim 9, wherein at least one of the data processing units is portable, and wherein the memory is in the portable one of the data processing units.
 12. A method of defining communication modes between data processing units, the method being performed by a memory of one of the data processing units, the memory including a data structure that defines the communication modes and that includes a, possibly empty, set of data elements that are either permanently stored or computed, the method comprising the steps of:receiving a communication primitive that is a defined value and is accepted as a command from another of the data processing units at an external interface list in the data structure, the communication primitive including a first set of data references; accessing from the external interface list a procedural description in the data structure that defines procedures to be performed by the one data processing unit in response to the command using the set of data elements; using a second set of data references in the data structure to refer to the set of data elements, the second set of data references being associated with the procedural description and first access conditions controlling access to the data elements in the set of data elements such that the set of data elements is available when the procedures defined in the procedural descriptions are performed and the first access conditions are met; and using the first set of data references to access a data list in the data structure that has second access conditions controlling access to the data elements in the set of data elements and a third set of references to the set of data elements, the third set of references being accessible by the first set of data references through the second access conditions, the data elements referenced by the third set of references being used by the procedural description associated with the communication primitive.
 13. The method of claim 12, wherein the memory has stored therein first executable program code elements of the procedures defined in the procedural description, and wherein the data structure further includes second executable program code elements of the procedures defined in the procedural description, the method further comprising the step of using the first and second code elements to execute the procedures defined in the procedural description.
 14. The method of claim 12, wherein at least one of the data processing units is portable, and wherein the memory is in the portable one of the data processing units.
 15. A method of defining communication modes between data processing units, the method being performed by a memory of one the data processing units, the memory including a data structure that includes at least one application program and a, possibly empty, set of data elements that are either permanently stored or computed, the at least one application program including at least one interaction context that defines the communication modes and including first access conditions controlling access to the data elements in the set of data elements, the method comprising the steps of:receiving a communication primitive that is a defined value and is accepted as a command to enter the interaction context from another of the data processing units at an external interface list in the interaction context, the communication primitive including a first set of data references; accessing from the external interface list a procedural description in the interaction context that defines procedures to be performed by the one data processing unit in response to the command using the set of data elements; using a second set of data references in the interaction context to refer to the set of data elements, the second set of data references being associated with the procedural description and the first access conditions such that the set of data elements is available when the procedures defined in the procedural description are performed and the first access conditions are met; and using the first set of data references to access a data list in the interaction context that has second access conditions controlling access to the data elements in the set of data elements and a third set of references to the set of data elements, the third set of references being accessible by the first set of data references through the second access conditions, the data elements referenced by the third set of references being used by the procedural description associated with the communication primitive.
 16. The method of claim 15, wherein the memory has stored therein first executable program code elements of the procedures defined in the procedural description, and wherein the at least one application program further includes second executable program code elements of the procedures defined in the procedural description, the method further comprising the step of using the first and second code elements to execute the procedures defined in the procedural description.
 17. The method of claim 15, wherein at least one of the data processing units is portable, and wherein the memory is in the portable one of the data processing units.
 18. The method of claim 15, wherein the at least one application program further includes a further interaction context, the method further comprising the steps of:receiving a further communication primitive that is a further defined value and is accepted as a further command to enter the further interaction context from another of the data processing units at a further external interface list in the further interaction context, the further communication primitive including a fourth set of data references; accessing from the further external interface list a further procedural description in the further interaction context that defines procedures to be performed by the one data processing unit in response to the further command using the set of data elements; using a fifth set of data references in the second interaction context to refer to the set of data elements, the fifth set of data references being associated with the further procedural description and the first access conditions such that the set of data elements is available when the procedures defined in the further procedural description are performed and the first access conditions are met; and using the fourth set of data references to access a second data list in the further interaction context that has third access conditions controlling access to the data elements in the set of data elements and a sixth set of references to the set of data elements, the sixth set of references being accessible by the fourth set of data references through the third access conditions, the data elements referenced by the sixth set of references being used by the further procedural description associated with the further communication primitive. 